Automotive brake disks are periodically machined using a disk brake rotor lathe in order to remove any warping or other variation that has presented itself during thousands of miles of use. The disk brake rotor lathe typically comprises a pair of cutting arms that are placed against the surfaces of a disk brake rotor and moved radially along the surfaces at a desired depth of cut to remove the warpage and return the surface to more planar configuration.
The process of moving the cutting arms radially while pressed against the opposing surfaces cause vibrations that both produce undesirable high decibel noise and chatter that inhibits the machining of the rotor surfaces to a suitable degree of planarity. Accordingly, it is desirable to attenuate these vibrations to both reduce the risk of damage to the ears of workers within earshot of an operating lathe and to more ensure a higher quality more planar rotor surfaces.
Several dampening devices are known in the art, such as described in U.S. Pat. Nos. 3,710,661; 4,178,819; 4,531,434; 5,297,460; 6,227,085; 6,591,720 ('720); 6,865,972; and 7,114,420 ('420), all of which suffer from one problem or another that has prevented the devices from being adopted by many brake rotor mechanics.
The prior art device taught in the '720 patent is illustrative. Like many of the prior art devices it comprises a thin gauge wire (approximately ⅛″ in diameter or thereabouts) bent into a u-shape that acts to at least partially bias opposing friction pads attached to the wire's ends towards each other. The biasing force helps keep at least a portion of the pads in contact with opposing surfaces of the brake rotors as the rotors are being machined. In practice, the biasing force does not hold the pads against the rotors tightly enough to prevent much of the undesirable vibration. Accordingly, many variations of this type of vibration attenuating device include coiled springs spanning between the arms of the u-shaped wire to provide additional biasing force. To prevent the spring from sliding down the arms which are typically canted towards each other, the steel arms are often coated with a plastic covering to increase the friction between the ends of the spring and the arms. However, the spring cannot be so stiff as to prevent a user from easily pulling the pads apart to place the device over a brake rotor. Unfortunately, a spring that is compliant enough to permit ease of use does not provide enough biasing force to prevent vibration in many instances. Furthermore, through extensive use the plastic cover often wears away causing the spring to slide down the arms when the device is in use and thereby reducing the biasing force as the spring unloads.
The forgoing problem concerning the auxiliary coil spring seems to have been the basis for replacing the spring with a rigid clip in the '420 patent, which describes a device similar to that in the '720 save for the spring to clip substitution. It can be appreciated that the clip does greatly increase the biasing load; however, the clip can be difficult to actuate and as such may not be adopted by many brake rotor machinists. Even when a clip is used, the ultimate load that may be applied by the prior art device is limited somewhat be the relatively low flexural stiffness of the u-shaped wire and the relatively low bending moment created along the wire between the clip and the pads.
Ultimately, because of the issues and problems associated with the prevailing prior art designs, rotor machinists have tended not to use the prior art vibration attenuating devices even when the devices are available to them.